There are certain types of shoes in which it is necessary that the bottom of the shoe does not deform while the shoe is being worn. This is the case, for example, with shoes designed for use in certain sports such as cycle racing, hockey and also in the boots for use with roller skates.
In such cases, it would be possible to achieve the necessary rigidity by inserting a hard, stiff insert of metal or the like in the bottom of the shoe to give it the necessary stability. However, this is not easily done because a metal insert would not be able to form a continuous structure with the remaining constituents of the shoe bottom. Additionally, it is only possible to a very limited extent to thread screws into a thin metal insert incorporated into a shoe bottom for attaching the remaining apparatus necessary for the particular sport such as, for example, in a roller skate or ice skate.